Because of the almost complete destruction of the helicopter by the crash and fire, it could not be determined whether any pre-impact failure or system malfunction contributed to this accident; however, none was identified. The evidence gathered at the crash scene was similar to that of a weather-related accident where the pilot becomes disoriented and loses control of the helicopter due to the lack of visual cues. However, the reported weather from persons in the local area provides no supporting evidence that unusual weather patterns were present on the afternoon of the occurrence. There is insufficient medical information available to determine the influence of the 25 September 1997 jet fuel inhalation incident and the subsequent toxic effects which may have acted on the liver, the respiratory, cardiovascular, and immune systems. The possibility that atherosclerotic coronary artery disease caused the pilot to lose consciousness and/or to be disorientated and, subsequently, to lose control of the helicopter could not be conclusively ruled out. The following Engineering Branch reports were completed: LP 170/97 - Instrument Examination LP 171/97 - Helicopter Components Examination LP 176/97 - Engine Components ExaminationAnalysis Because of the almost complete destruction of the helicopter by the crash and fire, it could not be determined whether any pre-impact failure or system malfunction contributed to this accident; however, none was identified. The evidence gathered at the crash scene was similar to that of a weather-related accident where the pilot becomes disoriented and loses control of the helicopter due to the lack of visual cues. However, the reported weather from persons in the local area provides no supporting evidence that unusual weather patterns were present on the afternoon of the occurrence. There is insufficient medical information available to determine the influence of the 25 September 1997 jet fuel inhalation incident and the subsequent toxic effects which may have acted on the liver, the respiratory, cardiovascular, and immune systems. The possibility that atherosclerotic coronary artery disease caused the pilot to lose consciousness and/or to be disorientated and, subsequently, to lose control of the helicopter could not be conclusively ruled out. The following Engineering Branch reports were completed: LP 170/97 - Instrument Examination LP 171/97 - Helicopter Components Examination LP 176/97 - Engine Components Examination Records show that the pilot was certified and qualified for the flight in accordance with existing regulations. Records show that the helicopter was certified and equipped in accordance with existing regulations and approved procedures. Most of the the helicopter was destroyed by the impact forces and the post-crash fire. Examination of the components revealed no mechanical deficiencies that would have contributed to the accident. The engine was determined to be developing substantial power at impact. Postmortem examination revealed no residual effects from the aspiration-type chemical-induced pneumonia resulting from jet fuel inhalation. The pilot had advanced coronary artery disease.Findings Records show that the pilot was certified and qualified for the flight in accordance with existing regulations. Records show that the helicopter was certified and equipped in accordance with existing regulations and approved procedures. Most of the the helicopter was destroyed by the impact forces and the post-crash fire. Examination of the components revealed no mechanical deficiencies that would have contributed to the accident. The engine was determined to be developing substantial power at impact. Postmortem examination revealed no residual effects from the aspiration-type chemical-induced pneumonia resulting from jet fuel inhalation. The pilot had advanced coronary artery disease. The cause of the loss of control of the helicopter that led to a steep right-bank and nose-down descent to the ground could not be determined.Causes and Contributing Factors The cause of the loss of control of the helicopter that led to a steep right-bank and nose-down descent to the ground could not be determined.